It is known that particularly effervescent granules consisting of citric acid and sodium bicarbonate or sodium carbonate are relatively highly sensitive to atmospheric humidity, This is also true of systems in which sodium citrates are used with alkali metal bicarbonates and/or carbonates.
For instance, U.S. Pat. No. 5,415,870 teaches to simultaneously incorporate tartaric acid in the surface of citric acid carrier crystals. The crystal surface can be doped with tartaric acid and then be allowed to react with carbonates and/or bicarbonates.
Moreover, U.S. Pat. No. 5,527,540 suggests to use tartaric acid as carrier for effervescent system particles, Therefore sodium carbonate and sodium bicarbonate are embedded on crystalline tartaric acid and in powdered tartaric acid by granulation, whereupon the granules are covered with a solution of tartaric acid and EDTA.
Effervescent systems which are prepared using monosodium tartrate with alkali metal bicarbonates and/or carbonates are known to have improved properties, especially with respect to the sensitivity to atmospheric humidity. On the other hand, monosodium tartrate is very expensive.
Attempts have now been made to produce monosodium tartrate by reacting tartaric acid with sodium carbonate and bicarbonate by means of surface reactions.
Such surface reactions lead to mixed systems comprising monosodium tartrates and disodium tartrates. It has now surprisingly been found that relatively large amounts of monosodium tartrate are formed in surface reactions of this type, and it would have to be assumed that they give very slow effervescent systems.
On the other hand, it has been found that relatively substantial reaction of tartaric acid and resulting relatively large amounts of monosodium tartrate give very rapid effervescent systems which furthermore exhibit previously unknown stability to atmospheric humidity.
It was found, surprisingly, that the tartaric acid, which is converted to monosodium tartrate, with sodium bicarbonate gives surprisingly short dissolution times and in particular is stable to atmospheric humidity of 80% for 6 days or more.
The granules which are produced in the reaction of tartaric acid and sodium bicarbonate and sodium carbonate were scientifically investigated in order to clearly find out which salts predominantly occur and what is the reason for the insensitivity to moisture.